Method and apparatus for the production of sheet glass

ABSTRACT

Process and apparatus for improving the smoothness and planarity of a sheet or ribbon of glass having a surface temperature of about 780* to 920* C. and having a viscosity of the order of 106.5 to 105 poises just before passing to and between a pair of metallic spaced smoothing and reducing rollers maintained uniformly at a surface temperature selected from a range of about 400* to 650* C. and by which the ribbon is reduced to 75 percent to 95 percent of its thickness prior to entry between the rollers. The surface temperature of the rollers is selected inversely as the temperature of the glass, within the ranges stated, and as shown upon the graph of Figure 1.

United States Patent Tissier 1 51 Apr. 11, 1972 [54] METHOD ANDAPPARATUS FOR THE 1,519,314 1924 Koupal ..65/253 PRODUCTION OF SHEETGLASS 27:32; fonei ....6535526)3( amni et a 5 [721 Invenm Tissie"saimcobaini France 3,218,141 11/1965 Lambert ..65/83 x [73] Assignee:Compagnie De Saint-Cobain, Neuilly-surs i France jnrnarylgamzrzersl.zLte)on lliaihorc'ie J sslstant xammero ert 1n say, r. [221'Flled: 1969 Attorney-Dale A. Bauer, John L. Seymour and Bauer and 21Appl. No.: 851,905 Seymour 57 ABSTRACT Foreign Application Priority Data1 Process and apparatus for lmprovlng the smoothness and Aug. 27. 1968France ..l64244 planarity of a Sheet or ribbon of glass having a Surfaceperature of about 780 to 920 C. and having a viscosity of the [52] U.S.Cl "665521, 2695/ 6655/ 130516, order of 106.5 to 5 poises just beforepassing to and between 1 l 5/ C05) 1/3/18 a pair of metallic spacedsmoothing and reducing rollers maing #i'i 355 356 tained uniformly at asurface temperature selected from a f 1 g g -g 01 i/48 range of about400 to 650 c. and by which the ribbon is reduced to percent to percentof its thickness prior to entry between the rollers. The surfacetemperature of the rol- [56] References cued lers is selected inverselyas the temperature of the glass, within UNITED STATES PATENTS the rangesstated, and as shown upon the graph of Figure 1. 1,413,766 1922 Myers..65/101 9 Claims, 4 Drawing Figures PATENTEDAPR 11 m2 3. 655,355

sum 2 [1F 3 //v VENTOR Pierre Tissier A T'TORNE Y5 PATENTEDAPR 11 I9723.655355 sum 3 OF 3 FIG.4.

INVENTOR Pierre Tissier ATTORNEYS METHOD AND APPARATUS FOR THEPRODUCTION OF SHEET GLASS This invention relates to a method of andmeans for the production of sheet glass by rolling.

In the past, serious difiiculties have arisen in the manufacture ofsheet glass by procedures such as drawing and/or rolling, because ofsurface defects in, and lack of planarity and smoothness of thecompleted product.

In the usual prior art procedure the glass flows or is drawn from theforehearth or draw pot of a melting tank, by and between rollers bywhich the incipient sheet is smoothed and reduced to sheet form of thedesired thickness. I have found that because of temperature differencesin and along the aforesaid rollers, corresponding differences inviscosities of the glass are effected which may cause localirregularities in thickness of the sheet, and which may be of the orderof tenths of a millimeter. Such differences in viscosities may alsocause local variations in the composition of the glass and these mayfurther contribute to corresponding differences in thickness andsmoothness of the completed glass.

Further, one of the principal drawbacks in the production of sheet glassby lamination, resides in defects of planarity of the glass ribbon,after it has passes in contact with and between the relatively coolsurfaces of the laminating rollers. It is not possible to avoid or toeliminate such defects merely by raising the temperature of the rollersbecause such a procedure increases the tendency of the glass to adhereto the rollers and may thus create further defects.

In French Pat. No. 1,409,806, it is proposed to improve the planarity ofthe surfaces of the glass ribbon being formed, by subjecting it whileplastic to the action of smoothing rollers having about the same surfacetemperature as the incipient ribbon. But after such procedure it is alsonecessary to remove from the surfaces of the ribbon, particles which areessentially infusible and which otherwise adhere to the hot glass ratherthan to the rollers themselves, and thus create surface irregularitiesin the finished glass.

The present invention enables, and has for its chief object, a methodand apparatus by which the completed sheet glass has a planarityequivalent to that of a sheet after it has been ground and polished byprior art procedures.

A further object is to provide a method and apparatus wherein theaforesaid result is attained with roller temperatures materially belowthat at which particles adhere to the sheet. There is thus avoided theproblems inherent when such particles or detritus are distributed overand embedded in the surfaces of the sheet or ribbon and which must befinally eliminated as by grinding and polishing. the rollers Inconformity with the present invention the sheet glass in a coolingprocedure, is passed between smooth planing rollers having a line ofcontact with the glass uniformly at about 400 to 650 C., the glassitself being cooled to about 780 to 920 C. The rollers define betweenthem a space about 75 percent to 95 percent of the thickness of theglass just before it enters between them.

It is also possible to start the novel method with sheet glasspreviously formed and which is accordingly reheated to the temperaturerange above stated. The temperature has to be measured by an opticalpyrometer because, due to its relatively low or poor heat conductivitythe central portions or layers of the glass are hotter than its surfaceareas.

The temperature ranges given are valid for glass of compositions usuallyemployed in production by lamination, such for example as:

SiO, 70 to 73% AI O; to 3% Na,0+l(,0 13.5 to 15.5% CaO+MgO 11 to 14%Other ingredients 0 to 3% When glass is employed having a compositionessentially different from that given in the preceding table, acorresponding change in temperature is utilized from the range of 780 to920 C., which as stated, is for glass having a viscosity of the order of10 5 to 10 poises, such as is ordinarily used in glass formed by drawingor laminating. It has been found that if the temperature thus measuredis below 780, the efficiency of the method is deleteriously affected andthe quality of glass produced is materially lowered. On the other hand,when the temperature measured as aforesaid, is higher than 920 C.,defects as above mentioned crop out, such as marking or marring of thesheet. At such higher temperatures, that is, above 920 C. there is alsothe added risk that the glass may adhere to the rollers and effectcorresponding surface defects.

Within the aforesaid temperature limits the surfaces of the glass sheetare relatively stiff or rigid with respect to the more plastic innerlayers or portions thereof. These inner layers are therefore morereadily subject to small displacements which result in a ready transferof glass in the central layers located under a protrusion orprotuberance. In other words, when such a protrusion passes between therollers, an elevated pressure is created below it; and this higherpressure causes a minute transfer of the center or core layers of theglass, to a contiguous location where the pressure is less intense. As aresult of this action the mean thickness of the ribbon remainsessentially unchanged. When a sheet of glass laminated in accordancewith prior art procedures, has deviations from true planarity, of theorder of 0.1 mm or more, the method of the present invention is alsohighly useful to effect a reduction of such deviations to a valuematerially less than 0.1 mm. In the examples subsequently given it waspossible to obtain a smoothness wherein the aforesaid deviations areless than 0.01 mm with respect to an area of between about I and 30 cmGlass having a temperature and being processed as previously explained,is introduced between smooth reducing rollers, which may be of metal.The hot glass in passing between these rollers, produces a certainheating of their surfaces. However, the ends of the rollers wouldotherwise run at a temperature or temperatures below their centralportions. In conformity with the present invention, to remedy thistemperature difference and to maintain the surface temperature of therollers constant throughout their length, the central portions arecooled while their end portions are supplied with supplemental heat, asby electrical resistance heaters. The temperature of the roller surfacesshould be carefully regulated to remain within the range 400 to 650 C.,as previously explained.

The foregoing and other objects and advantages of the invention willbecome clear to those skilled in the art, after a study of the followingdetailed description, in connection with the accompanying drawingdepicting apparatus by which the invention may be carried into practice,and which is to be taken in an illustrative rather than a limitingsense.

In the drawing:

FIG. 1 is a graph showing as abscissas the surface temperature range ofthe laminating rollers and, as ordinates, the corresponding range ofoptimum temperatures of the glass entering between the rollers;

FIG. 2 is a vertical longitudinal section showing schematically anapparatus for practicing the invention;

FIG. 3 is a perspective view showing in greater detail the apparatus ofFIG. 2; and

FIG. 4 is a central axial section through one of the two identicalrollers shown upon FIGS. 2 and 3.

Referring in detail to the drawing and in particular to FIGS. 2 and 3, aribbon of glass 1 is formed by drawing from a mo]- ten supply 2contained within the forehearth 3 of the melting tank, a portion ofwhich is identified at 4. The glass passes over refractory lip 5 of theforehearth and then to and between a first pair of spaced parallellaminating rollers 6, 7, driven by power means not shown. These rollersare smoothsurfaced and cooled in a known way by circulation of water orother coolant through their hollow interiors.

On emerging from between rollers 6, 7 the incipient ribbon passes over anumber of supporting rolls 8 which as indicated upon FIG. 3, may bedriven from roller 7 by chain or belt means 9 passing about a sprocketor pulley 10 fixed to the bearing shaft of the roller, and passing abouta number of small sprockets or pulleys 11 each fixed to the bearingshaft of a respective one of rolls 8. The effective diameters of pulley10 on the one hand, and pulleys 11 on the other, will be such that rolls8 are driven at the same linear speed as rollers 6 and '7. Alternativelyrolls 8 may be replaced by a gas cushion support for the glass, formedby a multiplicity of upwardlydirected gas jets distributed over the areaof the ribbon to be supported, as taught by French Pat. No. 1,527,937.

The incipient ribbon next passes to and between a second pair of rollers12, 13. At the instant the glass enters between these rollers, itsaccurately-measured surface temperature is about 780 C. These rollersmay have the same diameter and axial dimension of, for example, 0.40 mand 1.60 m, respectlvely. Because of its good wearing qualities andrelatively low cost, perlitic cast iron is an excellent material formaking these rollers, which have smooth polished surfaces. FIG. 4 showsone of these rollers 12, 13, in axial section as subsequently described.

Continuing with FIG. 3, lower roller 13 is joumaled in bearing blocks14, 15 fixed in frame 16. This frame has uprights or ends 17, 18 eachprovided with a slot or opening having parallel vertical guide edgessuch as are indicated at 19, 20 for upright 18. Each pair of guide edgesreceives with a smooth guiding fit, a respective one of two slides 21,22, so that each slide is guided for smooth accurate verticaltranslation.

Each slide 21, 22 is equipped with a journal for the respective ends ofshaft 23 of roller 12. The shaft of lower roller 13 is identified at 24.Shafts 23, 24 are driven by variable speed power means of known type andhence not shown. The linear sped of these rollers will be adjusted, ofcourse, for the speed of travel of the ribbon and the reduction inthickness thereof which they effect.

Vertical jacks which may be of the screw type are fixed at the top endsof uprights 17, 18 and are identified at 25, 26. The threaded shaft ofeach jack is connected as by a thrust bearing, with a respective one oftwo slides 27, 28 each of which is guided for smooth accurate verticaltranslation by and between the guide edges of its upright.

Confining attention to slide 28, a thrust rod 29 is pivoted at its upperend 30, to slide 28 and at its lower end, at 31, to slide 22. Likewisethrust rod 32 positioned with the slot of upright 17, is pivotallyconnected at 33, 34 to sides 21 and 27, respectively. Rods 29 and 32 arerigidly interconnected near their lower ends, by brace rod 35. Upperslides 27, 28 are like wise interconnected by brace rod 36.

Spacer or gage blocks 37, 38 are provided. For example, block 38 isinterposed between its slide 22 and bearing 14. Likewise, spacer block37 is located between slide 21 and bearing 15. These blocks incooperation with jacks 25, 26, positively hold rollers 12, 13 spaced adistance determined by the thickness of the blocks and thereforeestablish the reduction in thickness effect upon the ribbon by therollers. For instance, if the ribbon on emerging from between rollers 6,7 has a thickness of about 1.5 mm, the spacing of rollers 12, 13 will beabout 1.2 mm, thus effecting a reduction in thickness of the order of20percent. Under such conditions the jacks exert a force, each of about3.5 metric tons for a ribbon of glass of the width mentioned. Rollers12, 13 have an arc of contact with the glass of about percent. Theirlinear speed is preferably about 9.5 m/min., corresponding to astretching or attenuation of the ribbon between the two pairs ofrollers, of about percent.

After emerging from between rollers 12, 13 the ribbon reexpandsappreciably to recover a thickness of about 1.5 mm and 1,400 mm width,that is, about the same dimensions as before passing to and betweenthese rollers. A gas cushion support 39, FIG. 2, supports the ribbon asit emerges from between rollers 12, 13, until it is essentially solidand passes to annealing means generally identified at 40.

FIG. 4 shows in detail the construction of lower roller 13, it beingunderstood that upper roller 12 may be of like construction. The centralcylindrical portion 40 has an axial bore 41 counterbored at its ends asat 42, 43, to receive end journal bearing members 44, 45 respectively,having reduced outer ends and rigidly fixed as by threading to portion40. Packing such as 46 is compressed within the space in eachcounterbore, between its end wall and the corresponding bearing members44, 45.

Bore 41 is provided with disc-like partitions 47, 48 axially spaced andwhich effectively divide the bore into three compartments 49, 50 and 51wherein different thermal conditions are maintained as previouslyindicated.

From the right end of roller 13 as viewed upon FIG. 4, a stationary pipe52 passes axially through a bore in journal member 45, throughcompartment 49, into compartment 50. Cooling air introduced underpressure at 53, flows through the pipe directly into the central part ofcompartment 50 where it is directed radially into peripheral contactwith the bore in this compartment and then flows through a labyrinth ofpassageways defined by a coaxial system of cylindrical baffles asgenerally identified at 54. The construction is such that cooling air isdivided and passes in opposite directions from the central part ofcompartment 50, toward both ends and in surface contact with thecorresponding portion of bore 41. Air then passes radially inwardlythrough central apertures in partition 48.

As shown upon FIG. 4, this partition has a baffle 55 surrounding theaforesaid apertures and connected at its left end with exhaust tube 56which passes axially to the left through compartment 51 and at its leftend connects with an aligned tube 57 passing axially and freely throughthe bore in journal member 44 to the exterior thereof. Exhausted airescapes through holes 58 in the walls of tube 57, exteriorly of journalmember 44.

End compartments 49 and 51 enclose resistance heater elements 59, 60,respectively. Element 59 is fed from slip rings 61 fixed to the rollerjournal member 45 and from which conductors 62, 63 lead in and along thebore of the journal member, to heater 59. Likewise at the left end ofthe roller 13, current is led to heater element 60, from slip rings 64connected with conductors 65, 66 extending centrally through journalmember 44. By these means, positive control the temperature of therollers 12 and 13 is effected so that their surface temperature isessentially constant at the preferred value of 600 C., as measured by anoptical pyrometer, actually a type R F, Land pyrometer.

l have found that better results are attained when the uniform surfacetemperature of the rollers thus attained, is adjusted inversely as thetemperature of the glass. Thus, for a glass temperature of about 780 Cit is preferable to maintain the surface temperature of the rollers atabout the maximum, for example 620 C., while when the glass is about 920C., it is preferable to maintain the surface temperature of the rollersat about the minimum, for example 450 C. The graph of FIG. 1 shows theaforesaid relation wherein abscissas represent the temperature of therollers in degrees centigrade, and ordinates represent surfacetemperature of the glass to the same scale, as it enters between therollers 12, 13. By using the graph it is possible to select the optimumtemperature of the rollers for any particular surface temperature of theglass within the range given. The graph was prepared for a roller havingdiameter of about 400 mm 15.75 inches).

The following examples are by way of illustration only and are not to betaken in a limiting sense.

EXAMPLE 1 Glass is melted in a tank 4 and rolled by an apparatusessentially as depicted upon FIG. 2. The glass has the followingcomposition by weight percentages:

s10, 71 .0 rep, 0. 1 CaO 1 1.0 M30 3.0 Na,O+-K,O 14.0

SO; A1

The molten glass of the aforesaid composition melted in tank 4, flowsover refractory forehearth lip 5 and is laminated between rollers 6, 7,cooled by an internal flow of fluid. The incipient ribbon thus formedhas a width of about 1,400 mm and a thickness of about 1.5 mm. It passesover supporting means 8 such as rollers or, preferably, a cushion of gascreated by apparatus of the type disclosed in French Pat. No. 1,527,937,to and between smoothing and reducing rollers 12, 13. When the incipientribbon enters between these rollers its temperature as measured by aLand, optical pyrometer type R. U., is about 780 C. The rollers areabout 0.40 m in diameter and 1.6 m long. They are smooth surfaced andmay be of perlitic cast iron.

EXAMPLE 2 Using the same apparatus as in Example 1, the incipient glassribbon is formed by and between rollers such as 6, 7. On entrancebetween the second pair of rollers 12, 13, the ribbon has a width ofabout 1,400 mm, a thickness of about 4 mm and a surface temperature ofabout 840 C. The surface temperature of rollers 12, 13 is about 550 Cand they are spaced by about 3.7 mm. The force exerted by each of thetwo jacks 25, 26 is of the order of 2.5 metric tons. Rollers 12, 13 havea linear speed of about 4 m/min. The corresponding speed of rollers 6, 7is about 3.6 m/min. The reduction of thickness effected by rollers 12,13 is therefore about 10 percent. After passing rollers 12, 13, theresulting ribbon has a width of about 1,410 mm and a uniform thicknessof about 4 mm.

EXAMPLE 3 Using the same apparatus as in Examples 1 and 2, the incipientribbon of glass emerging from rollers 6, 7 has a thickness of about 12mm and a surface temperature of 920 C. at which temperature it passes tosmoothing rollers 12, 13 whose surface temperature is about 450 C. Theselatter rollers are spaced about 1 1.3 mm. The force applied to theribbon is simply that due to the weight of roller 12 alone. The linearspeed of rollers 12, 13 is about 1.3 m/min., and that of rollers 6, 7about 1.15 m/min. Immediately before entering between rollers 12, 13 theribbon has a thickness of about 12 mm. The width of the ribbon afterpassing rollers 12, 13, is about 1,420 mm and a corresponding slightdiminution of thickness is effected.

Glass produced by the present method is exceptionally smooth and free ofwaviness, undulations and other surface defects. Instead of forming theincipient ribbon by and between rollers 6, 7, it may be formed bydrawing or by the well-known tin flotation procedure.

Other changes, modifications and substitutions will become obvious tothose skilled in the art, after a study of the preceding disclosurewhich is therefore to be taken in an illustrative sense only.

lclaim:

1. The method of smoothing the surfaces of sheet glass by passing thesame between rollers, comprising, passing incipient sheet glass at afirst surface temperature within about the range 780 to 920 C., andhaving a viscosity of the order of 10 5 to 10 poises to and between apair of smoothing and reducing rollers, while maintaining thetemperature of the rollers at and throughout their lines of contact withthe glass, at a second uniform temperature within the range of about 450to 600 C., said first and second temperatures being determined inaccordance with the graph of FIG. 1, within the ranges specified.

2. The method of claim 1, said first and second temperatures, inaccordance with the graph of FIG. 1, having a sum which is essentially aconstant between about 1,350 and 1,400.

3. The method of forming sheet glass comprising, passing molten glass toand between a first pair of reducing rollers to form an incipientribbon, passing the incipient ribbon at about 780 to 920 C., and havinga viscosity of the order of 10 5 to 10 poises to and between a secondpair of smoothing rollers, while maintaining the surface temperature ofthe second pair of rollers along their lines of contact with the glass,at about 450 to 600 C., said surface temperature being selected as thedifference between a constant numerical value of about 1,350

to 1,400, and the temperature of the incipient ribbon aforesaid.

4. The method of claim 3, maintaining the surface temperature of thesecond pair of rollers constant along their lines of contact with theglass, by cooling the central portions thereof while supplying heat tothe end portions thereof.

5. Apparatus for smoothing sheet glass, comprising, a frame, a pair ofspaced parallel smoothing rollers journaled in said frame to receive andsmooth the sheet between them, said rollers being tubular, partitionmeans within each said roller dividing the same into a discrete centralcompartment and dis crete first and second end compartments at andwithin the respective ends of each said roller, conduit means connectedwith one end of each said roller for supplying coolant to said centralcompartment thereof, and heater means within each said end compartment,for supplying heat to the peripheral surfaces of said rollerscorresponding to said end compartments.

6. The apparatus of claim 5, said conduit means including a first pipeextending axially into and through one end of each said roller and intosaid central compartment, there being apertures in said first pipe fordischarging coolant radially into the central portion of said centralcompartment, said conduit means also including a second pipe forexhausting coolant from said central compartment, axially thereofthrough the other end of said roller, and baffie means in said centralcompartment directing coolant in each axial direction from saidapertures, into contact with the roller peripheral surface correspondingto said central compartment, thence to said second pipe.

7. The apparatus of claim 6, said heater means comprising first andsecond electric heaters in each said end compartment, respectively.

8. The apparatus of claim 5, means journaling one said roller on an axisfixed with respect to said frame, means mounting the other said rollerfor guided translation toward and from said one roller, to vary thespacing therebetween, gage block means each positioned between thejournals at the respective ends of said rollers and determining thespacing between them, and jack means connected with said other roller,to vary the force exerted on said gage block means.

9. The method of claim 1, said glass having the ingredients by weight:SiO to 73%; Na O K 0 13.5 to 15.5%; Ca0 MgO 1 l to 14%; Al O up to 3%;other ingredients up to 3%.

2. The method of claim 1, said first and second temperatures, inaccordance with the graph of FIG. 1, having a sum which is essentially aconstant between about 1,350 and 1,400.
 3. The method of forming sheetglass comprising, passing molten glass to and between a first pair ofreducing rollers to form an incipient ribbon, passing the incipientribbon at about 780* to 920* C., and having a viscosity of the order of106 5 to 105 poises to and between a second pair of smoothing rollers,while maintaining the surface temperature of the second pair of rollersalong their lines of contact with the glass, at about 450* to 600* C.,said surface temperature being selected as the difference between aconstant numerical value of about 1,350 to 1,400, and the temperature ofthe incipient ribbon aforesaid.
 4. The method of claim 3, maintainingthe surface temperature of the second pair of rollers constant alongtheir lines of contact with the glass, by cooling the central portionsthereof while supplying heat to the end portions thereof.
 5. Apparatusfor smoothing sheet glass, comprising, a frame, a pair of spacedparallel smoothing rollers journaled in said frame to receive and smooththe sheet between them, said rollers being tubular, partition meanswithin each said roller dividing the same into a discrete centralcompartment and discrete first and second end compartments at and withinthe respective ends of each said roller, conduit means connected withone end of each said roller for supplying coolant to said centralcompartment thereof, and heater means within each said end compartment,for supplying heat to the peripheral surfaces of said rollerscorresponding to said end compartments.
 6. The apparatus oF claim 5,said conduit means including a first pipe extending axially into andthrough one end of each said roller and into said central compartment,there being apertures in said first pipe for discharging coolantradially into the central portion of said central compartment, saidconduit means also including a second pipe for exhausting coolant fromsaid central compartment, axially thereof through the other end of saidroller, and baffle means in said central compartment directing coolantin each axial direction from said apertures, into contact with theroller peripheral surface corresponding to said central compartment,thence to said second pipe.
 7. The apparatus of claim 6, said heatermeans comprising first and second electric heaters in each said endcompartment, respectively.
 8. The apparatus of claim 5, means journalingone said roller on an axis fixed with respect to said frame, meansmounting the other said roller for guided translation toward and fromsaid one roller, to vary the spacing therebetween, gage block means eachpositioned between the journals at the respective ends of said rollersand determining the spacing between them, and jack means connected withsaid other roller, to vary the force exerted on said gage block means.9. The method of claim 1, said glass having the ingredients by weight:SiO2 - 70 to 73%; Na2O + K2O - 13.5 to 15.5%; CaO + MgO -11 to 14%;Al2O3- up to 3%; other ingredients up to 3%.